Fedora. There’s a video of him explaining why he uses Fedora instead of Debian.
Edit: Link to Fedora’s pages and a Youtube video on why Linus does not use Debian (or debian-based distros)
https://fedoraproject.org/wiki/Is_Fedora_For_Me#Other_People_Using_Fedora




Can you run lsblk within the emergency shell? Sounds a bit like the HDD has taken theplacde of /dev/sdb, upon which there’s no second partition nor a root filesystem -> root device not found.